Engine cooling systems can have an air-type cooling arrangement or a liquid-type cooling arrangement. Due to the higher heat capacity of liquids, however, it is possible for significantly greater quantities of heat to be dissipated using a liquid-type cooling arrangement than is possible using an air-type cooling arrangement. Therefore, internal combustion engines are frequently equipped with a liquid-type cooling arrangement to accommodate ever increasing engine thermal loads. For example, it is common for internal combustion engines to include a supercharger coupled to the engine system that is densely packaged in the engine compartment. This results in an ever greater number of components being integrated into the cylinder head or cylinder block, and further increases the thermal loading of the internal combustion engine.
In a liquid-type cooling arrangement the cylinder head is equipped with at least one coolant jacket, including coolant ducts to circulate the coolant through the cylinder head. In this arrangement, the heat is discharged to the coolant in the interior of the cylinder head surface, and therefore does not have to first be conducted to the cylinder head surface in order to be dissipated, as is the case in an air-type cooling arrangement. The heat which is discharged to the coolant is thereby extracted from the coolant again outside the cylinder head, for example by a heat exchanger and/or in some other way as it is circulated throughout the coolant system by a pump arranged in the coolant circuit. In a similar manner, the cylinder block may also have one or more coolant jackets that allow heat to be discharged to the coolant as it flows through the cylinder block. To form a coolant circuit, the outlet-side discharge openings via which coolant is discharged from the coolant jackets are connected to the inlet-side supply openings which serve for the feed of coolant via a recirculation line.
To reduce the friction losses and thus the fuel consumption of an internal combustion engine, fast heating of the engine oil, in particular after a cold start, may be advantageous. Fast heating of the engine oil during the warm-up phase of the internal combustion engine ensures a correspondingly fast decrease in the viscosity of the oil and thus a reduction in friction and friction losses, in particular in the bearings which are supplied with oil, for example the bearings of the crankshaft.
Methods and concepts are known wherein the friction losses are reduced by fast heating of the engine oil. For example, the oil may be actively heated by an external heating device. However, a heating device is an additional consumer of fuel, which opposes a reduction in fuel consumption. Other example concepts provide that the engine oil heated during operation be stored in an insulated vessel and utilized upon a restart, but the oil heated during operation cannot be held at a high temperature for an unlimited amount of time, which is problematic. In yet another example, during the warm-up phase, a coolant-operated oil cooler may be utilized, contrary to its intended purpose, for heating the oil.
In order to reduce friction losses, fast heating of the engine oil may also occur in response to the fast heating of the internal combustion engine itself, which in turn is assisted, or forced, by extracting as little heat as possible from the engine during the warm-up phase. In this respect, the warm-up phase of the internal combustion engine after a cold start is an example of an operating mode in which it is advantageous for as little heat as possible, and preferably no heat, to be extracted from the internal combustion engine. Therefore, control of the liquid-type cooling arrangement in which the extraction of heat after a cold start is reduced for the purpose of fast heating of the internal combustion engine may be realized through the use of a temperature-dependent self-controlling valve, often referred to as a thermostat valve.
In an internal combustion engine which has both a liquid-cooled cylinder head and a liquid-cooled cylinder block, it is advantageous for the flow of coolant through the cylinder head and the cylinder block to be controlled independently of one another, in particular because the two engine components are thermally loaded to different degrees and exhibit different warm-up behavior. In this regard, it may be advantageous for the coolant flow through the cylinder head and the coolant flow through the cylinder block to be controlled in each case by a dedicated thermostat valve.
The German laid-open specification DE 100 61 546 A1 describes a cooling system for an internal combustion engine, which is cooled by liquid coolant, and wherein the amounts of coolant which flows firstly through coolant ducts of a cylinder head and secondly through coolant ducts of a cylinder block are predefined. Therein, the thermostat valve of the cylinder head has a lower opening temperature than the thermostat valve of the cylinder block, which are both positioned downstream of the engine components. This method, however, requires two shut-off elements or thermostat valves and therefore increases the system costs, the space required and the overall weight of the engine system. A further disadvantage is that the circulation of the coolant in the cooling circuit cannot occur in a targeted manner, even after a cold start of the internal combustion engine. For example, after a cold start, coolant is conducted through both the cylinder head and also through the cylinder block, although the coolant flow through the cylinder block is reduced to a small leakage flow.
Herein, the inventors have recognized that control of a liquid-type cooling system is sought wherein the amount of circulating coolant can be reduced after a cold start in a targeted manner and that further allows thermal management of the internal combustion engine as it heats up to operating temperatures. Therefore, herein a self-controlling thermostat valve is described having an invariant, component-specific operating temperature suitable for all load states, and which has an opening temperature configured for high thermal loads, which is comparatively low and leads to relatively low coolant temperatures even in partial-load operations.
For example, different coolant temperatures may be advantageous for different load states because the heat transfer in a cylinder head or cylinder block is determined by the amount of coolant flowing therein, in addition to the temperature difference between the engine component and the coolant. Thus, a relatively high coolant temperature in partial-load operation is substantially equivalent to a small temperature difference between the coolant and the cylinder head or cylinder block. The result is a reduced heat transfer at low and medium loads, which increases the thermal efficiency in partial-load operations.
The inventors have further recognized that the purpose of a liquid-type cooling arrangement is not to extract the greatest amount of heat from the internal combustion engine under all operating conditions. Rather, what is sought is a demand-dependent control of the liquid-type cooling arrangement, which aside from full load also makes allowance for the operating modes of the internal combustion engine in which it is more advantageous for less heat, or as little heat as possible, to be extracted from the internal combustion engine.
Therefore, according to one example aspect of the disclosure, an internal combustion engine having a control arrangement for the liquid-type cooling circuit in which both the coolant flow through the cylinder head and through the cylinder block is controlled at the outlet side by a single setting element, or adjustable control valve is described. Since a single control unit containing a thermostat valve is used instead of two thermostat valves, advantages are offered with respect to cost reduction, weight and the space required for inclusion in the coolant circuit. Another advantage is that the number of components in the engine system is also reduced, which may further reduce the procurement costs and assembly costs of the engine system, and thereby shorten the assembly time.
Within the context of the present disclosure, the expression “internal combustion engine” encompasses diesel engines and spark-ignition engines and also hybrid internal combustion engines. It should also be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.